package horstmann.ch02_mail;
import java.util.ArrayList;

/**
   A first-in, first-out collection of messages. This
   implementation is not very efficient. We will consider
   a more efficient implementation in chapter 3.
 */
public class MessageQueue
{
	/**
      Constructs an empty message queue.
	 */
	public MessageQueue()
	{
		queue = new ArrayList<Message>();
	}

	/**
      Remove message at head.
      @return message that has been removed from the queue
	 */
	public Message remove()
	{
		return queue.remove(0);
	}

	/**
      Append message at tail.
      @param newMessage the message to be appended
	 */
	public void add(Message newMessage)
	{
		queue.add(newMessage);
	}

	/**
      Get the total number of messages in the queue.
      @return the total number of messages in the queue
	 */
	public int size()
	{
		return queue.size();
	}

	/**
      Get message at head.
      @return message that is at the head of the queue, or null
      if the queue is empty
	 */
	public Message peek()
	{
		if (queue.size() == 0) return null;
		else return queue.get(0);
	}

	private ArrayList<Message> queue;
}